Adding and Deleting Object Own Properties

This section provides a quick description of object's own properties. A tutorial example is provided on how to add, update, and delete object's own properties.

When you create a new object from the "Object" constructor, you will get an object with only two default properties:

But you can add more properties to one object at any time using an assignment operation like this:

object_name.property_name = initial_value;

The added property is for this one object only. Other objects will not have this property.

You can also delete properties from one object at any time using a delete operation like this:

delete object_name.property_name;

Here is a tutorial example that shows you how to add a new property, update the property value, retrieve the property value, and delete a property.

<html>
<!-- Object_Property.html
   Copyright (c) 2013 by Dr. Herong Yang, herongyang.com
-->
<head>
<title>Object Properties of "Object"</title>
</head>
<body>
<pre>
<script type="text/javascript">

   // Creating objects of "Object" type
   var mySite = new Object();
   var myBook = new Object();
   
   // Adding a new property to one object only
   mySite.url = "herongyang.com";
   myBook.author = "Herong Yang";

   // Updating a property value
   mySite.url = "www.herongyang.com";

   // Showing property values
   document.writeln('mySite.url: '+mySite.url);
   document.writeln('myBoot.url: '+myBook.url);
   document.writeln('mySite.author: '+mySite.author);
   document.writeln('myBook.author: '+myBook.author);

   // Is this property for one object only?
   document.writeln('mySite.hasOwnProperty("url"): '
      +mySite.hasOwnProperty("url"));

   // Deleting a property from one only
   document.writeln('Deleting mySite.url...');
   delete mySite.url;
   document.writeln('mySite.url: '+mySite.url);
</script>
</pre>
</body>
</html>

The result matches my expectation:

mySite.url: www.herongyang.com
myBoot.url: undefined
mySite.author: undefined
myBook.author: Herong Yang
mySite.hasOwnProperty("url"): true
Deleting mySite.url...
mySite.url: undefined

Table of Contents

 About This Book

 Introduction to JavaScript

 ECMAScript Language Specification and JavaScript Dialects

 Data Types, Variables and Expressions

 Flow Control Statements

 Creating, Accessing, and Manipulating Arrays

 Defining and Calling Functions

 Web Browser Supporting JavaScript

 Server-Side and Client-Side Web Scripting

Introduction to Objects

 What Is an Object?

 Objects of "Object" Data Type

Adding and Deleting Object Own Properties

 Adding and Deleting Object Own Methods

 Using "this" Keyword to Represent Current Object

 Object Literals of the "Object" Type

 Objects and Associate Arrays

 Objects with Indexed Properties

 Differences between "Object" and "Array"

 Using "Array" Objects as "Object" Objects

 Defining Your Own Object Types

 Inheritance of Properties and Methods through the Prototype Object Chain

 'jrunscript' - JavaScript Shell Command from JDK

 Using Functions as "Function" Objects

 Introduction to Built-in Object Types

 W3C's Document Object Model (DOM) Specifications

 References

 PDF Printing Version